Exam 4 Key

Multiple Choice

Identify the choice that best completes the statement or answers the question.

1. Looking at a spiral galaxy face-on reveals that the spiral arms are much more apparent (visible) and blue than the rest of the disk. Why?

a.	The spiral arms are the only feature in the disk.
b.	The spiral arms have a much lower density of dark matter.
c.	The spiral arms have a much lower density of gas and dust.
d.	The spiral arms contain a higher density of O- and B-type stars.
e.	The spiral arms contain a higher density of Population II stars.

2. The location of the turn off point in an H-R diagram of a globular cluster is affected by:

a.	The distance to the globular cluster
b.	The mass of the globular cluster
c.	The age of the globular cluster
d.	The size of the globular cluster
e.	The number of stars in the globular cluster

3. Which statement about star formation is false?

a.	Gravity is the principal force causing a cloud of gas to contract and eventually form stars.
b.	Star formation is an ongoing process in our Galaxy even though the Galaxy itself formed about 12 billion years ago.
c.	In a newly formed group of stars, the K- and M-type stars outnumber the O- and B-type stars.
d.	A massive, cool, and dense molecular cloud is the type of interstellar medium that is most likely to begin forming stars soon.
e.	A less-massive star forms faster than a more-massive star.

4. This phenomenon that occurred in the early Universe was proposed to address the three problems associated with standard big bang cosmology: the horizon problem, the flatness problem, and the matter-antimatter asymmetry problem. What phenomenon is it?

a.	Inflation
b.	Deflation
c.	Creation
d.	Transmutation
e.	Annihilation

5. What is a pulsar?

a.	It is a type of main sequence star that periodically ejects from its surface large quantities of hot gas
b.	It is a neutron star observed by pulses of radiation
c.	It is a type of main sequence star that periodically changes its size
d.	It is a type of supergiant that periodically changes its surface temperature
e.	It is a type of black hole that actually emits radiation in the form of radio pulses

6. Which process correctly describes a pair production?

a.	A photon changes into a proton and neutron
b.	A photon changes into an electron and proton
c.	A photon changes into two photons
d.	A photon changes into two electrons
e.	None of the above

7. What is the difference between a G2V and G2I stars?

a.	The first one is a main sequence star and the second is a white dwarf.
b.	The first one is a main sequence star and the second is a supergiant.
c.	The first one is composed of hydrogen and the second of helium.
d.	The first one is much hotter than the second.
e.	The first one more luminous than the second.

8. From what evidence do astronomers deduce that the Universe is expanding?

a.	They observe that the number of globular clusters increases with time.
b.	They detect a redshift in the spectral features of distant galaxies.
c.	They observe the edge of the Universe moving away from us.
d.	They observe that distant galaxies dissolve, being pulled apart by the expansion of space.
e.	They detect a cosmic wind caused by the expansion of space.

9. What is the value of Ù₀ if the universe is flat?

a.	2.7
b.	300,000
c.	75
d.	9.81
e.	1

10. The evolution of a binary star may differ from that of a single star because:

a.	Two stars are more massive than one star.
b.	Two stars are more luminous than one star.
c.	Two stars are hotter than one star.
d.	One star may transfer mass to the other.
e.	The binary orbital motion of the stars affects their motions on the H-R diagram.

11. Which observations are required to determine the distance to a Cepheid variable star?

a.	Average apparent brightness and average temperature
b.	Average apparent brightness and mass
c.	Period and average color
d.	Average apparent brightness and period
e.	Radial velocity and period

12. One practical application of Hubble’s law is measuring __________ of distant galaxies.

a.	Colors
b.	Rotational velocities
c.	Distances
d.	Masses
e.	Intrinsic shapes

13. What two gases contribute the most to the chemical composition of the interstellar medium?

a.	Methane and ethane
b.	Ammonia and argon
c.	Hydrogen and carbon monoxide
d.	Hydrogen and oxygen
e.	Hydrogen and helium

14. According to the Big Bang theory for the formation of the Universe, the Universe:

a.	Never formed – it has always existed
b.	Formed in the state of high temperature and low density
c.	Formed in the state of low temperature and high density
d.	Formed in the state of low temperature and density
e.	Formed in the state of high temperature and density

15. A white-dwarf supernova is a good standard candle for distance measurement for all of the following reasons except one. Which one is it?

a.	All white-dwarf supernovae involve explosions of stars of nearly the same mass.
b.	A white-dwarf supernova is so bright that it can be detected even in very distant galaxies.
c.	A white-dwarf supernova can only occur in a globular cluster.
d.	The light curve of a white-dwarf supernova is distinct from that of a core-collapse supernova allowing astronomers to distinguish between the two.
e.	The spectrum of a white-dwarf supernova is distinct from that of a core-collapse supernova allowing astronomers to distinguish between the two.

16. What process could directly lead to the formation of a neutron star?

a.	Core-collapse supernova
b.	Carbon detonation supernova
c.	Helium flash in a red giant
d.	Merger of two black holes
e.	Triple alpha process

17. What type of interstellar medium produces 21-cm radiation?

a.	Cool atomic hydrogen
b.	Hot and ionized hydrogen
c.	Cool atomic helium
d.	Hot carbon dust grains
e.	Cool iron dust grains

18. Which of the following statements about the cosmic microwave background radiation is false?

a.	It has a temperature of about 3 degrees Kelvin.
b.	It had a higher temperature in the past.
c.	It is the result of a mixture of radiation from many independent sources, such as stars, galaxies, and nebulae.
d.	It is a relic radiation of the Big Bang.
e.	It appears essentially isotropic.

19. The Milky Way galaxy is part of:

a.	The Virgo Cluster
b.	The Large Magellanic Cloud
c.	The Small Magellanic Cloud
d.	The Fornax Cluster
e.	None of the above

20. Which part of the electromagnetic spectrum allows the most efficient searches for intelligent life in the Universe?

a.	Gamma ray
b.	Optical
c.	Radio
d.	Ultraviolet
e.	X-ray

21. Astronomers think that dark matter exists because:

a.	They can detect it with radio telescopes.
b.	The outer parts of galaxies rotate faster than expected on the basis of the material visible in them.
c.	The existence of dark matter is the only way to explain black holes in quasars.
d.	The existence of dark matter resolves the “missing helium” problem.
e.	All of the above

22. Which one of the following galaxies would contain the smallest fraction of its mass in the form of gas and dust?

a.	E7
b.	SBa
c.	SBb
d.	Sc
e.	Sa

23. Which pair of objects in the Solar System is of great interest to those searching for past and present forms of life?

a.	Mercury and Venus
b.	Mercury and the Moon
c.	Mars and Europa (one of Jupiter’s moons)
d.	Pluto and its moon, Charon
e.	Phobos and Deimos, the moons of Mars

24. Absolute magnitude of a star is the measure of the star’s:

a.	Mass
b.	Luminosity
c.	Temperature
d.	Color
e.	Distance

25. The value of Hubble’s constant is close to:

a.	75 km/s/Mpc
b.	-75 km/s/kg
c.	100 kg/m/s
d.	5 Gyr
e.	1

26. If the force due to gas pressure were larger than the force of gravity in the interior of a star, the star would:

a.	Increase its density
b.	Increase the rate of nuclear reactions in its core
c.	Not change at all
d.	Expand
e.	Contract

27. Five main sequence stars with spectral types O5, G8, M1, B2, and F7 formed at the same time. Which one of these five stars will evolve off the main sequence first?

a.	O5
b.	G8
c.	M1
d.	B2
e.	F7

28. Which statement about black holes is always true?

a.	Black holes are made of dark matter
b.	Black holes do not rotate
c.	Within the event horizon, the escape velocity is larger than the speed of light
d.	Theoretical models show that black holes more massive than 100 solar mass may not exist
e.	Black holes may not exist. If they did, they would suck in all of the matter in the Universe

29. What is z?

a.	Hubble’s constant
b.	Gravitational constant
c.	Radius of the Universe
d.	Location of the Milky Way in the Universe
e.	Redshift

30. What kind of spectrum does the cosmic microwave background radiation have?

a.	An absorption spectrum
b.	A synchrotron spectrum
c.	A black body spectrum
d.	A bremsstrahlung spectrum
e.	An emission spectrum

31. A star seen through the interstellar medium appears redder than it really is. Why?

a.	Dust in the interstellar medium magnetically deflects blue photons more than red photons.
b.	Dust in the interstellar medium scatters and absorbs blue photons more than red photons.
c.	Dust in the interstellar medium scatters red photons more than blue photons.
d.	Dust in the interstellar medium adds red photons to the light from the star.
e.	Dust in the interstellar medium gravitationally deflects blue photons more than red photons.

32. What happened when the Universe was about 300,000 – 400,000 years old?

a.	The strong nuclear force and the weak nuclear force decoupled from each other.
b.	The Universe became transparent as atoms formed.
c.	It was the end of the “nuclear” epoch when most of the helium in the Universe was produced.
d.	Galaxies and clusters began to form.
e.	We don’t know - this is one of the unsolved mysteries in modern cosmology.

33. The fate of our Sun is that it will eventually become a:

a.	Brown dwarf
b.	White dwarf
c.	Black hole
d.	Pulsar
e.	Neutron star

34. What phenomenon do astronomers rely on when measuring the line-of-sight (radial) velocity of a star?

a.	Intensification of spectral features in the star’s spectrum
b.	Shift in wavelength of spectral features in the star’s spectrum
c.	Narrowing of spectral features in the star’s spectrum
d.	Broadening of spectral features in the star’s spectrum
e.	Weakening of spectral features in the star’s spectrum

35. Nuclear fusion reactions require high temperature because:

a.	The nuclei then move slowly enough that they stick when they collide.
b.	The nuclei then move slowly enough that they collide frequently.
c.	The heat energy is converted to mass by E=mc^2.
d.	The nuclei then move quickly enough to overcome their mutual electric repulsion.
e.	The heated nuclei must melt and merge together.

36. What is the habitable zone?

a.	The range of distances from a star within which liquid water can exist on the surface of an Earthlike planet.
b.	The range of regions on a planet where life can exist.
c.	The range of regions in the Milky Way where planets around stars can form.
d.	The range of distances from a star within which a terrestrial (i.e., rocky) planet can exist.
e.	The range of distances from a star within which ozone can exist in a planet’s atmosphere.

37. What is proper motion of a star?

a.	It is a quantity that states the maximum allowed speed the star can have.
b.	It is an apparent motion of the star on the sky, in units of angle per time, due to the Earth’s rotation.
c.	It is a quantity that states the speed of the star as a fraction of the speed of light.
d.	It is a quantity that states how fast and in what direction the star is moving.
e.	It is motion of the star on the sky, in units of angle per time, due to the star’s transverse velocity (velocity component perpendicular to the line of sight).

38. The Miller-Urey experiment produced:

a.	DNA
b.	AC/DC
c.	Bacteria
d.	Amino acids
e.	Proteins

39. What happens when a degenerate gas in a rigid container is heated?

a.	The temperature increases and the pressure remains the same.
b.	The temperature and pressure decrease.
c.	The temperature and pressure remain the same.
d.	The temperature increases and the pressure decreases.
e.	The temperature decreases and the pressure increases.

40. Astronomers were able to map the distribution of galaxies and clusters of galaxies in space up to a distance of about 200 Mpc (approximately 600 million light-years). The distribution is:

a.	Random everywhere.
b.	Not random. The distribution shows a filamentary structure, surrounding vast, nearly empty voids.
c.	Not random. The distribution shows that most galaxies are in the north celestial hemisphere and very few in the south celestial hemisphere.
d.	Random in the north celestial hemisphere and not random in the south celestial hemisphere.
e.	Not random. The distribution shows that most galaxies form a ring around the Milky Way.